1. Field of the Invention
The present invention relates to a radar apparatus using an FMCW system, and more particularly, it relates to a technique for avoiding false detection of a reflecting object due to “false frequency components” in a beat signal processing part.
2. Description of the Related Art
In radar apparatuses using a conventional FMCW system, there has been known a technique that synthesizes an antenna beam by applying digital beam forming (hereinafter referred to as “DBF”) processing to individual beat signals obtained from a plurality of receiving parts, and also there has been proposed an apparatus that does not perform IQ detection but Ich detection alone (see, for example, a first patent document: Japanese patent No. 3780904 (page 4)).
In the conventional apparatus described in the first patent document, only the absolute value of a frequency component can be obtained for one received wave, and the plus or minus of the sign thereof can not be identified, so in order to solve this, the polarity or sign of the beat frequency is determined or identified by the following comparison processing (A) or (B).
(A): A comparison is made between the signs of changes (derivative) of the phase of the beat frequency during the increase and decrease of the sending frequency.
(B): A comparison is made between the signs of the phase differences in the beat frequency between two element antennas during the increase and decrease of the sending frequency.
Thereafter, a correct object detection result is obtained by inverting the sign (plus and minus) of the beam direction in accordance with the above-mentioned comparison result.
In the conventional radar apparatus, it is necessary to identify the polarity or sign of the beat signal frequency in an accurate manner, and unless the sign of the beat frequency could not be identified correctly, there would be a problem of misidentifying the sign of the beam direction, too.
In addition, in case where there exist a plurality of received waves, a plurality of frequency components are generated in each beat signal during the increase and decrease of the sending frequency, but there has been a problem that the sign of each beat frequency is not able to be correctly identified unless the beat frequencies of the individual received waves are correctly combined.